Slush molding permits molding without difficulty of complicated forms as undercut, deep drawing or the like, with the skin thickness kept uniform and at a high yield. On the strength of those advantages, the slush molding process has been widely practiced for molding various articles as interior component parts of motor vehicles. In this molding, soft polyvinyl chloride (PVC) powder has mainly been used as exemplified by unexamined Japanese Patent Publication No. H05-279485.
One problem is, however, that because of a high content of a low molecular weight plasticizer, the softened PVC loses its soft feel at temperatures below the solidifying point of the plasticizer. Other problems are encountered in service for a long time: (1) formation of oil film of evaporated plasticizer on the automobile front windshield, (2) loss in matting effect and soft touch as a result of migration of the plasticizer to the surface of the molded article, and (3) yellowing from the degradation of PVC with passage of time.
Efforts have been made to solve those problems, and there are known some improved versions. For example, modifications of PVC with flexible thermoplastic polyurethane resin are proposed as materials to provide soft touch without a low molecular weight plasticizer as disclosed in examined Japanese Patent Publication No. S53-29705, No. S59-39464 and No. S60-30688.
Yet, all those materials are based on PVC, and the fogging problem of molded articles remains to be solved. The automobile interior trims call for a better material than those prior art resins in thermal aging resistance and light aging resistance. The PVC-based materials have failed to satisfy the requirements.